1. Field of the Invention
The present invention relates to the detection of faults in underground electrical power cables.
2. Description of the Related Art
A conventional method used by electric utility companies and like facilities for isolating faults in underground power cable relies on a technician's observation of needle deflections that are induced within hand-held meters. Pulse signals generated by a capacitive discharge (CD), kenotron surge, or thyratron unit are transmitted along the cable under test and portions of the pulse signals are coupled into the hand-held meter through pick-up coils placed directly on the cable under test. Needle deflections at the pulse repetition frequency of the received pulse are observed by the technician. The cable portion beyond which the needle deflections are observed to drop off in amplitude is where the fault is assumed to lie.
The above-described conventional fault detecting method suffers from several disadvantages. For example, conventional hand-held meters are relatively sensitive to fluctuations in the background, and particularly to magnetic fields induced by currents in other nearby power cables. This leads to inaccurate detection, particularly in noisy urban environments. For example, within a typical urban, high noise background, needle fluctuations generally do not provide a user with the processing "history" needed to reject noise-induced false detections. Also, because the needle of the hand-held meters is deflected in response to a rectified signal, the polarity information inherent within the detected signal is destroyed. Further, because of the need to place the sensor head, i.e., pick-up coil, of a conventional unit directly on the faulted cable, the manhole at the test point must be cleared of water, other fluids, and debris. This is a lengthy and expensive procedure, particularly if the fluids are hazardous (e.g., PCB containing).